An animal's immune system is comprised of numerous elements that act separately and/or in concert to counteract, to eliminate, or to neutralize substances that are recognized by that system as foreign to the animal host. Generally, but not necessarily, the substance recognized as foreign by the immune system has its origin exogenous to the host. Exemplary of such exogenous substances are infectious bacteria and the by-products of their cellular activity, virus particles and their proteins, proteins injected by insect stings, and the like. In autoimmune diseases, such as rheumatoid arthritis, the host's immune system recognizes host-made proteins or self-made proteins as foreign.
The principal effectors of the immune system are the leukocytes, which include lymphocytes of thymic origin (T cells), lymphocytes produced in bone marrow (B cells), neutrophils which, inter alia, produce enzymes that make oxidizing agents such as hydrogen peroxide that have cytotoxic effects upon bacteria, and macrophages which present the foreign substance or antigen to the T cells, as well as produce a protein designated interleukin-1 that assists T cell transformation into T helper cells. Complement which is a complex mixture of proteins that acts in an ordered, cascading manner upon the foreign substance also plays a major role in immune responses.
B cells can be distinguished from T cells, inter alia, by the presence of immunoglobulins on their membrane surfaces. The immunoglobulins function as antibodies.
There are five known classes of immunoglobulins, identified as IgA, IgD, IgE, IgG, and IgM on the basis of five antigenically different heavy protein chains which in part make up the immunoglobulin molecule. B cells also bear non-immunoglobulin cell markers, including a complement receptor (CR), a receptor for the Fc portion of immunoglobulin (FCR), I-region associated antigens (Ia), and a set of differentiation antigens (Lyb 1-7) which are identified by all antisera and are correlated with various aspects of B cell maturation and activation. These markers are useful in phenotypically identifying B cells.
While the B cell immunoglobulins act upon the foreign substance, or antigen, the T cells, and particularly helper T cells, are believed necessary to stimulate B cells to divide and to differentiate into antibody secreting cells for humoral immunity. Supressor T cells contribute to the regulation of humoral immunity, while cytotoxic T cells and T cell mediators of delayed-type hypersensitivity are the principal effectors of cell-mediated immunity.
T cells include antigens designated Lyt 1, 2, and 3 that are related to T cell functions. Helper T cell precursors are of the Lyt 1.sup.+, 2.sup.-, 3.sup.- phenotype. It is these cells which normally participate in the activation and regulation of B cells.
Helper T cells are known to assist in activation and differentiation of immunoglobulin-secreting B cells after a first message is received by the B cells from the activating antigenic agent. However, the mode by which the T cells provide the second message of activation and differentiation to the B cells is a matter of controversy.
Guanosine-3', 5'-cyclic monophosphate (cGMP) has been implicated as a naturally occurring agent for providing the required second message. 8-Bromoguanosine-3', 5'-cyclic monophosphate (8-BrcGMP) has been found to be a weak synthetic intracellular lymphocyte mitogen.
The immune response can be modified by artificial supression (immunosuppression) or enhancement (immunopotentiation). Immunosuppression, i.e., artifically induced decreased responsiveness, can be achieved by six general methods: (1) administration of antigen, (2) administration of specific antisera or antibody, (3) use of other biologic reagents such as antilymphocyte antisera, (4) use of drugs or hormones, (5) radiation, and (6) surgical removal of lymphoid tissue. Immunopotentiation can include the administration of an agent effecting an increase in the rate at which the immune response develops, an increase in the intensity or level of the response, a prolongation of the response, or the development of a response to an otherwise non-immunogenic substance.
The agents which are known to enhance immune responses are generally termed adjuvants and can be placed into two general categories: (1) those providing general potentiation, i.e., substances which enhance both cellular and humoral immune responses for a wide variety of antigens, and (2) those providing specific potentiation, i.e., substances which enhance specific responses to certain antigens only.
Substances that can act as adjuvants can be grouped into the following categories: (1) water and oil emulsions, e.g., Freund's adjuvant, (2) synthetic polynucleotides, (3) hormones, drugs and cyclic nucleotides, (4) endotoxins, (5) lymphokines and monokines such as the interleukins.
A substance capable of specifically potentiating the immune response is transfer factor, a dialyzable leukocyte extract (DLE) obtained from human peripheral leukocytes. It has been reported that the transfer factor exhibits some effectiveness in patients with immunodeficiencies and possible effectiveness in cancer patients and in patients with limited immunodeficiencies. However, much remains to be learned about this particular substance.
In some diseases and physiological conditions such as X-linked agammaglobulinemias, senescence and drug-induced-immunosuppression, B cell activation and differentiation is lacking and/or exists only at a reduced level, thereby lessening the immune response of the host. These diseases and conditions are representative of immunosuppressed states. Here, enhanced activation and differentiation, if it can be effected, tends to beneficially lessen the disease manifestation and/or improve the patient's condition.
An immunopotentiated state can be illustrated by the bodily condition after vaccination. Here, the immune response is already enhanced due to an antigenic response, but could be beneficially enhanced still further to provide an improved degree and/or duration of immunity.
Neoplastic cell proliferation, including primary tumors and metastatic disease, typically can be explained as a manifestation of a cellular message that causes the cells to replicate without the normal regulatory restraints and/or at a much higher rate than is normal for the unaffected cells. One usual chemotherapeutic treatment for neoplastic diseases is to contact the neoplastic cells with low levels of materials that are generally cytotoxic in the hope that the general cytotoxicity will affect the rapidly replicating neoplastic cells to a greater extent than the normal cells and thereby selectively kill the rapidly replicating neoplastic cells. The drawbacks of such treatments include a general depression of many bodily functions, including loss of weight and hair, stomach and bowel disorders, and the like.
Interferons are a class of soluble, small proteins that inhibit virus multiplication. These proteins are produced by cells infected with substantially any animal virus particles or other viral agents, as well as by agents such as bacterial products and monoclonal antibodies. Interferons are cell-specific but not virus-specific. It would be beneficial in promoting an animal's general resistance to viral infection if the level of interferons present in the animal could be increased in the absence of naturally occurring (pathogenic) microbiological interferon-inducing agents.
In autoimmune diseases, the host recognizes its own proteins as antigens and, in essence, attacks itself through the production of antibodies to its own tissues. Since animals normally produce some antibodies to themselves (anti-self antibodies) whose effects are suppressed or tolerated, it is thought that autoimmune diseases may be a result of an overly active production of anti-self antibodies to which the usual suppression and/or tolerance-providing bodily mechanisms do not adequately respond. Such an over production of anti-self antibodies can be taken as analogous on the antibody level to the excess cellular proliferation exhibited by neoplastic cells.
Salicylates, such as acetyl salicylate (aspirin), are major chemotherapeutic agents for combatting autoimmune diseases such as rheumatoid arthritis. It is believed that the salicylates act to relieve the symptoms of rheumatoid arthritis by suppression of prostaglandin production and therefore their effect on the afflicted tissue. Chemotherapeutic agents such as gold, mercaptopurine and D-penicillamine have been utilized to treat rheumatoid arthritis, but some such drugs have toxic or teratogenic side effects, and their use has been associated with incidence of lymphoma and infection. It would therefore be advantageous to provide a chemotherapeutic agent that could be used to successfully treat autoimmune diseases without the above-noted side effects.
Lymphokines and monokines are immunopotentiating proteins produced by lymphocytes and cells of the monocyte-macrophage lineage respectively. One monokine, interleukin-1, is produced by macrophages when they are stimulated by a mitogen or antigen. Interleukin-1 is usually required for producing a primary antigenic response.
Interleukin-1 assists in the production of interleukin-2 in T cells. Interleukin-2 is a growth factor for T cells and assists in the transformation of T helper cells. Thus, induction of interleukin-1 production or of a protein-responsive activity on T cells similar to that produced by interleukin-1 would be beneficial in enhancing immune responses, particularly where macrophages are absent or where their interleukin-1 production is deficient.